1. Technical Field
The present invention relates in general to media disks and, in particular, to an improved system, method, and apparatus for performing metrology on the patterned magnetic media disks used in hard disk drives with integrated test pattern areas.
2. Description of the Related Art
Magnetic media such as the disks used in hard disk drives are typically constructed with concentric circular patterns of formations (e.g., lines, dots, etc.) that are on the order of nanometers in their dimensions. These formations on the patterned media must be qualified during manufacturing to ensure the quality and reliability of the product.
Patterned media may be evaluated with metrology technologies that utilize optical instruments based on spectroscopic ellipsometry or reflectometry. An alignment procedure typically is used for metrology and includes an additional pattern of one or more alignment marks. Alignment is required for pattern search and accurate measurement. These technologies precisely measure critical dimensions, sidewall angles, and multiple layer film thicknesses. The measurements are made on two-dimensional line and space structures, as well as three-dimensional hole and island structures. This technology produces accurate and precise models for production use of scatterometry results for both stand-alone and integrated metrology applications.
However, conventional metrology technologies only work in measuring formations that are arranged in rectilinear (e.g., rectangular, parallelogram-like, or hexagonal) patterns, rather than formations that have curvilinear periodicity such as those on magnetic media disks. In addition, the sizes of patterns, dots, and lines are too small to identify with the inspection techniques used by ellipsometry and x-ray refractivity. These techniques can only provide average dimensions for a periodic collection of islands. Moreover, SEM inspection techniques are slow, expensive and destructive to the sample being measured (i.e., because it requires the sample to be broken into smaller pieces, or because it contaminates the sample). This issue is becoming more significant as the data density (e.g., bits/nm2) in disk drives continues to increase.
As shown in FIG. 1, the regularity of features on magnetic media disks varies according to the radial position of the sample being analyzed on the surface of the disk due to the concentric circular patterns. For example, at sample 11, which is a laser spot having a diameter of 50 μm located at a radial distance of 0.3 inches from the disk center 13, the radius of curvature of the pattern of formations is far more pronounced than at sample 15, which is located at a radial distance of 1.25 inches from the disk center 13. Although current measurement technologies provide adequate metrology for some rectilinear formation patterns, they are not as well suited for curved formation patterns such as those in samples 11 and 15. Thus, an improved solution for measuring features that are arranged in curvilinear patterns would be desirable.